ARMI should be better at helping people identify what is a Pin

[john-science]

ARMI needs to provide a central interface for identifying a PIN.

1. First, beg / force / make people downstream use the PIN flag.
2. Provide a central ARMI function or two that return True / False if an ArmiObject is a PIN or not.

Some various thoughts here:

1. Downstream, I have seen literally dozens of different implementations of "is this a pin". And none of them are the same. That is a risk.
2. There is some "fun" here about things like "Is the wire/duct/whatever wrapped around a pin count as part of the pin?" That's solvable.
3. We could perhaps use grids on blocks to solve this problem.

(This ticket originated in this discussion.)

[john-science]

@keckler and @drewj-tp suggest that this ticket might be easier to do if we do the Composites can contain Composites ticket first.

I believe the idea is if Composites could contain Composites, then if there are 200 pins in a Block then we could make a PinComposite object type and ditch the mult parameter. And this would make it easier to ID a Pin, by just checking the composite type.